As climate change fuels drought, childhood immunizations may suffer

As climate change fuels extreme weather, one study suggests an increase in droughts could reduce rates of childhood vaccinations.

“It's kind of a surprising finding — and it's very important, because vaccines are just such an important intervention to save children's lives,” said Dr. Jason Nagata, a pediatrician and one of the authors of the study. “I think organizations need to be aware of how climate change can affect people's ability to access health care.”

The study, published in PLOS Medicine, listed potential drivers such as increased food insecurity, partner violence, declining mental health, increased migration, existing illness, and the weakening of public health infrastructures.

Decreased vaccinations

Drought is already linked to malnutrition, infectious diseases, and deteriorating mental health, but the study’s authors wrote that the link between drought and childhood vaccination rates is not yet well established.

The authors examined national health surveys and rainfall data in 22 sub-Saharan African countries, looking at the vaccinations of nearly 140,000 children born between 2011 and 2019. They looked at whether children born during a period of drought received vaccinations for bacillus Calmette–Guérin, or BCG; diphtheria–pertussis–tetanus, or DPT; and polio. They also looked at whether 1-year-old children living during a drought received measles vaccines.

The study found “drought was associated with lower odds of completion of childhood BCG, DPT, and polio vaccinations,” as well as first doses of the measles vaccine.

It found that when a child was born during a drought, there is a reduction of 1.5% points for BCG vaccination, reduction of 1.4% points for DPT vaccination, and a reduction of 1.3% points for polio vaccination in comparison to children that were not born during droughts. For 1-year-olds, there was a reduction of 1.9% points for receiving a measles vaccination during a drought compared to those at that age living without drought.

Percentage point reductions differ from percent decrease. For example, if 50% of children received their BCG vaccination in nondrought periods, and there is a 1.5% point reduction, it equals 48.5% during drought periods.

While these might sound like subtle changes, the percent decreases are for increments of time where drought is present, and these percentages would ultimately compound year after year, said Dr. Sheri Weiser, author of the report and co-director of the University of California's Center for Climate, Health and Equity. 

The vaccination rates found in the study were 70.6% for three doses of polio and 86% for BCG, while 57.6% of children over one years old receive all of their BCG, DPT, polio, and measles vaccines.

Nagata said that any reduction in vaccination rates is important, given how crucial this type of intervention is.

“Given that there are 400 million children currently living on the African continent, even small percentage reductions can represent millions of children,” Nagata said.

Results varied by country and some countries saw significantly steeper drops than the overall averages. For example, Rwanda saw almost a 30% point drop in measles vaccinations and Chad saw nearly a 20% point drop in polio vaccinations.

But in some countries, there was actually an uptick in vaccinations during droughts. For example, Zambia and Kenya saw an increase in BCG vaccination rates, and Gabon and Burundi saw increases in DPT vaccination.

The report theorized that in some countries that typically experience heavy rains, an increase in vaccinations may be because drought is less immediately disruptive to health care access than flooding.

The data examined is national level and not segregated by regions in each country that are more prone to drought, which could have seen larger reductions in the vaccination rates during these time periods, Weiser said.

Lives disrupted

The authors theorized a host of reasons driving these outcomes.

One is increased migration, as pastoralists and farmers move in search of greener pastures. Before a drought, a child might attend the same clinic, which kept their records and reminded them to return for their next shot.

“Whereas if they're moving all the time, they may not know where the nearest clinic is. And even if they do find the nearest clinic — that clinic doesn't have their previous records,” Nagata said.

Providing vaccinations to displaced populations is a challenge, as it's hard for authorities to forecast how many will be in a certain location at any point in time.

Existing illness could also result in missed vaccinations. Drought is associated with heightened acute malnutrition, fever, diarrhea, and cough. The researchers suggest parents might not vaccinate their child if they are ill — concerned it could accelerate symptoms or cause the child additional pain. “There's a perception the vaccine will make it worse for their kids,” Nagata said.

Home finances are another potential factor. With reductions in yields, families that are dependent on agriculture may have less money, which could make it harder to afford transportation to a clinic, or their time could be consumed by other efforts to scrounge together enough money to survive. Mental health might deteriorate during droughts and domestic violence might increase, creating additional barriers in a parent’s ability to juggle competing priorities in their lives.

“They may not be able to attend to other important things like going to health care visits,” Nagata said.

Extreme weather can also damage health facilities, such as droughts or heat waves sparking wildfires, or cutting electricity and power supplies. Vaccines need refrigeration.

Adjusting to extremes

“There is a very important need to prepare for the increasing negative impacts of extreme weather events and climate change on both health and on health care systems,” Weiser said.

Countries already worst affected by drought tend to be the same countries experiencing major challenges with immunization coverage because of fragile economies, civil strife, weak infrastructure, nomadic populations, displacement, and hard to access areas, said Dr. Richard Mihigo, coordinator of the immunization and vaccine development program at the World Health Organization’s regional office for Africa.

As climate change leads to more frequent droughts, Mihigo said he predicts that vaccination campaigns will need to adjust by better anticipating and tracking population movements. This has already been done, he said, as part of the polio eradication efforts in countries in the Sahel region, around the Lake Chad basin and in the Horn of Africa.

Satellite mapping of settlements was used to identify remote and unreached populations, as well as the movement of nomadic populations. WHO already works with countries with significant nomadic populations to coordinate vaccination outreach when these populations pass through areas at certain points of the year.

As the impacts of climate change accelerate, he said drought and climate change may affect the storage and movement of vaccines in rural areas.

Some countries have also managed to adapt their vaccination campaigns to extreme weather. A spokesperson for UNICEF said in South Sudan, where severe flooding is cyclical, vaccine strategies are impacted by rains, but mitigation efforts have helped vaccination rates remain relatively steady. The children’s agency and its partners pre-position vaccines during the dry season and map out where the flooding tends to displace people to plan for the vaccination activities in these locations in the lead up to the heavy rains.

And governments have also launched vaccine campaigns in response to droughts, according to Gavi, the Vaccine Alliance, including a measles vaccine campaign during the 2016 drought in Ethiopia, and a cholera vaccine campaign in Somalia the following year.